It is a widely known fact that compounds of organic coloring matters, such as the coloring matters for forming colored images in the field of photography, the organic dyes for dyeing fibers, and the coloring matters used in the area of printing, are liable to color-fading or discoloration by the effect of light. In view of this situation, various methods have been proposed for improving the color-fastness of such coloring matters against light.
One of such methods consists in a process characterized by the use of a certain kind of compound which improves the color-fastness of such a dye against light. For example, as the compounds which improve the fastness of colored images against light can be pointed out the hydroquinone derivatives mentioned in U.S. Pat. No. 2,360,290, No. 2,418,613, No. 2,675,314, No. 2,701,197, and so forth, the derivatives, such as chroman and chraman, which are mentioned in U.S. Pat. No. 3,432,300, No. 3,573,050, No. 3,574,627, No. 3,764,337, No. 3,574,626, No. 3,698,909, and No. 4,015,990, and the p-alkoxyphenols which are mentioned in U.S. Pat. No. 3,457,079 and No. 3,069,262, Japanese Patent Examined Publication No. 13496/1968, and so on.
Those compounds, however, were not necessarily satisfactory in terms of their effect. In the meanwhile, a technique for improving color-fastness against light by the use of a metallic complex is described in Japanese Patent Pulbication Open to Public Inspection Nos. 99340/1981, 168652/1981 and 51834/1985. (hereinafter referred to as Japanese Patent O.P.I. Publication). Among these metallic complexes, however, some had to be used in large quantities because their light-resisting effect was small. Some other such complexes were effective as a color-fastness improving agent working against light, and yet some of those had the shortcoming that the coloration of the metallic complexes themselves was so intense that they produce an effect of yellowish, yellowgreenish, or greenish coloring.
Above all, in case any such agent is used for photosensitive material for photography, any coloring of white areas will give considerable damages to aesthetic features, and such coloration will be a cause of a deterioration of the merchandise value.
Moreover, among such metallic complexes, there are some which causes an increase of fogging or staining by the effect of heat if such a complex is used for any silver halide photosensitive material for photography.
While conducting experiments up to the present time with respect to the metallic complexes hitherto known as such, we found that many of them were effective as color-fastness improving agents, but, as the coloration of such a metallic complex itself and an increase of fogging gave rise to a decrease of lightness, a change in hue, or a deterioration of the white-color areas in consequence of the occurrence of stain by the effect of heat, none of those complexes could be used with any satisfactory result unless some measure was taken for the settlement of the problem.
In view of these circumstances, we have been in continuous pursuit of a metallic complex which has a great color-fastness effect for organic coloring matter compounds, does not give any adverse effect to pictures, even if the complex is used as a color-fastness improving agent for colored images, because of the slightness of coloration in the metallic complex itself, or does not give any unfavorable influence resulting from an increase of fogging or the occurrence of stain even in case the complex is used for any silver halide photosensitive material for photography.